I have messed around with this idea a bit in the past and found that some UPS charge circuits become very unhappy with the low impedance load presented by a discharged capacitor bank. So besides charge balancing, some type of charge control should be added.

What capacitors did you use and did you collect any data from them? This is really what I am after.

I have not dug into the details for the UPS I plan to use beyond basic stuff to get a ballpark for the capacitors required. It's interesting that some of the SuperCaps will list UPSs as their targeted application.

How one can recommend a model if you don't want to post at least a power required. I could advise 10kVA model but would you want to pay for that (you could just buy Tesla Powerwall)?

If you take the time to read my first post, you will find I never asked about battery brands or UPS models. I never stated I needed extended my UPS to to have extended periods of uptime. This is all something you have brought up.

I am not asking you for a recommendation. You claim to have a combination/s that give you what you feel is an acceptable battery life. I am only asking that you document the specifics of that combination/s. If you keep records on battery life where you work, that also may be of interest for people looking for general information on UPS systems. I am not suggesting I will do anything with this data but others may find it helpful.

It would also be interesting to see some pictures of your UPS systems internals just to get a general idea about them. Maybe the next time you pull one down for service, you could post a few.

I have messed around with this idea a bit in the past and found that some UPS charge circuits become very unhappy with the low impedance load presented by a discharged capacitor bank. So besides charge balancing, some type of charge control should be added.

I'd not be too worried about balance; leakage is exponential with voltage so they self balance.

How one can recommend a model if you don't want to post at least a power required. I could advise 10kVA model but would you want to pay for that (you could just buy Tesla Powerwall)?

If you take the time to read my first post, you will find I never asked about battery brands or UPS models. I never stated I needed extended my UPS to to have extended periods of uptime. This is all something you have brought up.

You claim to have a combination/s that give you what you feel is an acceptable battery life. I am only asking that you document the specifics of that combination/s.

It's what you say now. Back then you asked for models I recommend. Why asking at all if not interested to begin with. What I can say that all our high power Riello UPS over various locations easily lasted 5+ years on the original set of batteries.

OK, not trying to be pedantic or a smart arse, but I suspect you mean four (4) batteries, to give a nominal 48 volt system. The standard lead acid 12 volt battery consists of six (6) cells. So what I suspect you have is 4 x 12V 7AH or such batteries. Therefore 24 cells with a charging float voltage of around 2.27 volts per cell so that the voltage across the battery bank is 54.5 volts. When a load is applied to the batteries, as when the input voltage fails and the UPS is called upon, the voltage across the battery bank, and therefore inverter input, will fall to approximately 50 volts and then stabilise. It will then only fall slowly until the battery end voltage is reached which is normally around 1.7 volts/cell or around 41 volts for the bank. At this end voltage the battery has basically given up all its energy and if it is allowed to keep running the voltage will 'fall off a cliff' very rapidly. Take it too far down and the battery can be irreparably damaged.

The inverter of the UPS will therefore be designed to operate within the extremes of the battery operational points, so 40 volts at the low end and 55 volts at the high end. So doing a quick BoE calc you'll find that about half of the energy stored in the capacitor is never going to get used, so you will probably need to take that into consideration when selecting the caps.

The other thing that you may need to take into account is the reaction time of the UPS. In this I mean how long does the UPS stay on battery power even with a short break. Many UPSs will have an extended time on battery even for the shortest of power outages. They may stay on battery power for ten (10) or Twenty (20) seconds even for a votage fail of only a few cycles. This hysteresis values varies between UPS manufacturers, so this would need to be verified before selection and sizing of any capacitor could take place.

It would also be interesting to see some pictures of your UPS systems internals just to get a general idea about them.

We only have old Powerware (now Eaton) 9120 series at the location where I am. In think one with the lowest power is 3kVa. I won't be taking them apart as they are in work, I cannot just randomly walk and take them apart. They use quality components.What I can say about APC is that they use cheap Chinese JH electrolytic capacitors, cheap relays and cheap batteries even in their expensive models.

Changing SLAs to supercaps would require a different charging circuit and a modified battery monitoring. It might be better to design a completely new supercap UPS. Another possibility to simply things is to go for a centralized 12V power supply since most SOHO network/telephone stuff is powered by 12V DC anyway (use DC/DC converters for other voltages). This would be also more efficient than using a cheap SMPSU wall warts for each device. BTW, be aware that some UPS' perform regular self-tests (mine does a 10s test every two weeks).

From my experience with running UPS' I can say that Panasonic SLAs run fine for about 5 years. They also have special SLAs for UPS usage which last longer but are also more expensive. If possible check and adjust the float voltage every few years because a too high voltage reduces the SLA's life span. APC's SmartUPS' have a hidden service menu for that and APC are also known to set the float voltage quite high. Sadly I have to agree that the quality of APC's UPS' went down and that their stickers for battery packs are quite expensive. Since they use Kung Long and other inexpensive brands I wouldn't buy any genuine replacement packs. The change of the control protocol to a top-secret one adds to the impression that APC's main goal became profit optimization. You have to buy a special translation module to be able to use a proper UPS management software.

I have messed around with this idea a bit in the past and found that some UPS charge circuits become very unhappy with the low impedance load presented by a discharged capacitor bank. So besides charge balancing, some type of charge control should be added.

I'd not be too worried about balance; leakage is exponential with voltage so they self balance.

Tim

I've seen some posts (other forums) where people have posted about leakage being all over the place with some of the cheap caps. I never see any specifics.

At some point I will need to have a look at the charger in the UPS I plan to use. I only looked at the open circuit voltage. With the UPS unplugged and unloaded, I measured the current draw and various thresholds where the UPS detects low battery, disables the output and eventually turns off. I based the capacitor size on the target up time max rated load for the UPS and the point where the UPS detects a low battery, plus some pad.

It seems very doable but like the video I linked, the person spent most of their time reverse engineering and changing the charging. I suspect this is going to be the problem in my setup as well.

I have messed around with this idea a bit in the past and found that some UPS charge circuits become very unhappy with the low impedance load presented by a discharged capacitor bank. So besides charge balancing, some type of charge control should be added.

What capacitors did you use and did you collect any data from them? This is really what I am after.

Before buying 35 supercapacitors for a 70 volt system, I did tests using a 100,000uF bank of aluminum electrolytics just to find out what modifications of the UPS charge circuits would be necessary. My test UPS was a Powerware Prestige EXT which uses an inconvenient 5x12V battery configuration.

Quote

I have not dug into the details for the UPS I plan to use beyond basic stuff to get a ballpark for the capacitors required. It's interesting that some of the SuperCaps will list UPSs as their targeted application.

They should be great for high reliability high power density line conditioners which is no surprise. The problem is that UPSes intended to use batteries expect a narrow operating voltage range.

The inverter of the UPS will therefore be designed to operate within the extremes of the battery operational points, so 40 volts at the low end and 55 volts at the high end. So doing a quick BoE calc you'll find that about half of the energy stored in the capacitor is never going to get used, so you will probably need to take that into consideration when selecting the caps.

Utilizing half of the energy of the capacitor is actually pretty good and what I would aim for minimum. Switching regulators are commonly designed to operate with a 2:1 input range (75%) but wide range 4:1 units (94%) also exist. A UPS intended to use supercapacitors would be designed to handle a wider input voltage range but most of the available energy is returned without going wild.

In a retrofit application, a wide input range high current boost converter could be used to extent the operating time but if you are already getting 50%, I would declare victory and move on.

AFAIK, good quality supercaps have a life span of about 10 years. My guess for the cheapies is 5 years.

This can be extended by voltage derating. Electrolysis of the electrolyte increases 10 times for every 0.4 volt increase in voltage and 30C increase in temperature. If you expect the capacitors to last more than 1 year, then do not operate them above 2.6 volts at 35C.

You claim to have a combination/s that give you what you feel is an acceptable battery life. I am only asking that you document the specifics of that combination/s.

It's what you say now. Back then you asked for models I recommend. Why asking at all if not interested to begin with. What I can say that all our high power Riello UPS over various locations easily lasted 5+ years on the original set of batteries.

Again, take the time to read. From my previous post:

Quote

I am not suggesting I will do anything with this data but others may find it helpful.

You may have felt I was looking for general help on UPSs and was offering your experience and advice but it was never my intent of the thread.

I have messed around with this idea a bit in the past and found that some UPS charge circuits become very unhappy with the low impedance load presented by a discharged capacitor bank. So besides charge balancing, some type of charge control should be added.

What capacitors did you use and did you collect any data from them? This is really what I am after.

Before buying 35 supercapacitors for a 70 volt system, I did tests using a 100,000uF bank of aluminum electrolytics just to find out what modifications of the UPS charge circuits would be necessary. My test UPS was a Powerware Prestige EXT which uses an inconvenient 5x12V battery configuration.

Quote

I have not dug into the details for the UPS I plan to use beyond basic stuff to get a ballpark for the capacitors required. It's interesting that some of the SuperCaps will list UPSs as their targeted application.

They should be great for high reliability high power density line conditioners which is no surprise. The problem is that UPSes intended to use batteries expect a narrow operating voltage range.

The inverter of the UPS will therefore be designed to operate within the extremes of the battery operational points, so 40 volts at the low end and 55 volts at the high end. So doing a quick BoE calc you'll find that about half of the energy stored in the capacitor is never going to get used, so you will probably need to take that into consideration when selecting the caps.

Utilizing half of the energy of the capacitor is actually pretty good and what I would aim for minimum. Switching regulators are commonly designed to operate with a 2:1 input range (75%) but wide range 4:1 units (94%) also exist. A UPS intended to use supercapacitors would be designed to handle a wider input voltage range but most of the available energy is returned without going wild.

In a retrofit application, a wide input range high current boost converter could be used to extent the operating time but if you are already getting 50%, I would declare victory and move on.

AFAIK, good quality supercaps have a life span of about 10 years. My guess for the cheapies is 5 years.

This can be extended by voltage derating. Electrolysis of the electrolyte increases 10 times for every 0.4 volt increase in voltage and 30C increase in temperature. If you expect the capacitors to last more than 1 year, then do not operate them above 2.6 volts at 35C.

I had stacked a few caps together when I first started to look at the UPS. I just don't have anything near large enough on hand. I do plan to derate them a fair amount.

I had read it and it was why I posted about the difference in the leakage currents. Did you measure their capacitance as well? ESR? I wonder how close some of these parts are to their specs.

By the way, ESR varies with time, much as it does with batteries. Though at least, I don't think this will be much of a problem at modest discharge rates. (Here, it should basically look like whatever the nominal ESR is.)

It is disgustingly apparent over long rates, however -- what would ordinarily be called dielectric absorption, is really ionic diffusion as charges equalize over the deeply porous (activated charcoal?) electrodes. So the leakage has a very long (days) tail, and the ratio of immediate capacity to full capacity (i.e., as measured at a discharge rate of, say, minutes versus weeks -- discounting leakage, naturally!) is surprisingly large, like 20 or 30% (i.e., the absorption recovery fraction).

The same effect, in batteries, limits how fast you can discharge, and especially charge, the chemistry.

On that note, an aside: I think it's neat to consider what's going on in batteries. At modest charge or discharge rates, behavior is linear, ionic diffusion isn't dominant, and efficiency is high. At high discharge rates, there is a large voltage drop through the electrolyte (and any semiconductors or insulators involved -- for example, lead dioxide is a semiconductor, and lead sulfate is an insulator), which saturates the reaction at the facing electrode surfaces, and drives more reaction deeper into the pores. The effect is, as you increase discharge rate, you get more and more current, albeit at less voltage -- less efficiency. This is great news for cold cranking applications, like cars and UPSs.

The opposite isn't true, though: when charging, the intended reaction has a lower overpotential, so it dominates at light charge rates. But a rapid charge quickly saturates the facing electrode surfaces, which undergo higher voltage reactions -- namely, the production of oxygen and hydrogen -- while the deeper pores continue to charge at a modest rate. This directly loses electrolyte solvent as gas (or recycles it, via catalyst, generating heat, in a sealed type), while the bubbles increase resistance further. I tested this recently, on a whim: a motorcycle-sized 12V lead acid battery can sustain over 60A discharge, keeping terminal voltage above 8V; but saturates quickly on charge, climbing to, say, 18V at only 20A. That was only a few seconds test, by the way.

I wouldn't recommend testing this in any lithium technology, for obvious reasons. The higher-voltage reactions (electrolysis of the solvent), and their consequences (gas buildup inside a sealed bag of pyrophoric chemicals, anyone?), are well known. The same physics ought to be relevant, though. This is good news for RC enthusiasts, but not so much for Tesla Motors.

Changing SLAs to supercaps would require a different charging circuit and a modified battery monitoring. It might be better to design a completely new supercap UPS. Another possibility to simply things is to go for a centralized 12V power supply since most SOHO network/telephone stuff is powered by 12V DC anyway (use DC/DC converters for other voltages). This would be also more efficient than using a cheap SMPSU wall warts for each device. BTW, be aware that some UPS' perform regular self-tests (mine does a 10s test every two weeks).

From my experience with running UPS' I can say that Panasonic SLAs run fine for about 5 years. They also have special SLAs for UPS usage which last longer but are also more expensive. If possible check and adjust the float voltage every few years because a too high voltage reduces the SLA's life span. APC's SmartUPS' have a hidden service menu for that and APC are also known to set the float voltage quite high. Sadly I have to agree that the quality of APC's UPS' went down and that their stickers for battery packs are quite expensive. Since they use Kung Long and other inexpensive brands I wouldn't buy any genuine replacement packs. The change of the control protocol to a top-secret one adds to the impression that APC's main goal became profit optimization. You have to buy a special translation module to be able to use a proper UPS management software.

Do you have any further info about this ?Some obscure service manual link maybe ?

This menu might even allow some tweaking of charging voltages to better suit various configurations of super caps.